Mars may be going through a period of climate change, new
findings from NASAs Mars Odyssey orbiter suggest.

Odyssey has been mapping the distribution of materials on and
near Mars surface since early 2002, nearly a full annual cycle
on Mars. Besides tracking seasonal changes, such as the advance
and retreat of polar dry ice, the orbiter is returning evidence
useful for learning about longer-term dynamics.

The amount of frozen water near the surface in some relatively
warm low-latitude regions on both sides of Mars' equator
appears too great to be in equilibrium with the atmosphere
under current climatic conditions, said Dr. William Feldman of
Los Alamos National Laboratory, N.M. He is the lead scientist
for an Odyssey instrument that assesses water content
indirectly through measurements of neutron emissions.

"One explanation could be that Mars is just coming out of an
ice age," Feldman said. "In some low-latitude areas, the ice
has already dissipated. In others, that process is slower and
hasn't reached an equilibrium yet. Those areas are like the
patches of snow you sometimes see persisting in protected spots
long after the last snowfall of the winter."

Frozen water makes up as much as 10 percent of the top meter
(three feet) of surface material in some regions close to the
equator. Dust deposits may be covering and insulating the
lingering ice, Feldman said. He and other Odyssey scientists
described their recent findings today at the fall meeting of
the American Geophysical Union in San Francisco.

High latitude regions of Mars have layers with differing ice
content within the top half meter (20 inches) or so of the
surface, researchers conclude from mapping of hydrogen
abundance based on gamma-ray emissions.

"A model that fits the data has three layers near the surface,"
said Dr. William Boynton of the University of Arizona, Tucson,
team leader for the gamma-ray spectrometer instrument on
Odyssey. "The very top layer would be dry, with no ice. The
next layer would contain ice in the pore spaces between grains
of soil. Beneath that would be a very ice-rich layer, 60 to
nearly 100 percent water ice."

Boynton interprets the iciest layer as a deposit of snow or
frost, mixed with a little windblown dust, from a cold-climate
era. The middle layer could be the result of changes brought
in a warmer era: The ice down to a certain depth dissipates
into the atmosphere. The dust left behind collapses into a soil
layer with limited pore space for returning ice.

Information from the gamma-ray spectrometer alone is not enough
to tell how recently the climate changed from colder to warmer,
but an estimated range might come from collaborations with
climate modelers, Boynton said.

Other Odyssey instruments are providing other pieces of the
puzzle. Images from the orbiter's camera system have been
combined into the highest resolution complete map ever made of
Mars' south polar region. "We can now accurately count craters
in the layered materials of the polar regions to get an idea
how old they are," said Dr. Phil Christensen of Arizona State
University, Tempe, principal investigator for the camera
system.

Temperature information from the camera system's infrared
imaging has produced a surprise about dark patches that dot
bright expanses of seasonal carbon-dioxide ice. "Those dark
features look like places where the ice has gone away, but
thermal infrared maps show that even the dark areas have
temperatures so low they must be carbon-dioxide ice."
Christensen said. "One possibility is that the ice is clear in
these areas and were seeing down through the ice to features
underneath."

Measurements by an instrument for monitoring the radiation
environment at Mars show the level of radiation hazard that
Mars-bound astronauts might face, including levels during a
period of unusually intense solar activity, said Dr. Cary
Zeitlin of the National Space Biomedical Research Institute,
Houston.

JPL manages Mars Odyssey for NASA's Office of Space Science,
Washington. Investigators at Arizona State University, Tempe;
University of Arizona, Tucson; NASA's Johnson Space Center,
Houston; the Russian Aviation and Space Agency, Moscow; and Los
Alamos National Laboratory, Los Alamos, N.M., built and operate
Odyssey science instruments. Information about the mission is
available on the Internet at: http://mars.jpl.nasa.gov/odyssey.